Process and apparatus for forming tapered spars



2 Sheets-Sheet l Hll {W TTORNEY v INVENTOR Edmund B. Cairns March 14, 1939.

v E. B. CAIRNS PROCESS AND APPARATUS FOR FORMING. TAPERED SPARS Filed Jl 11y 25, 1936 Y March 14, 1939. E. B. CAIRNS PROCESS AND APPARATUS FOR FORMING TAPERED SPARS Filed July. 25, 19:56 2 Sheets-Sheet, 2

I Lllmll l INVENTOR ldmandfl. Cairns ATTORNEYS Patented Mar. 14, 1539 t a UNITED STATES PATENT OFFICE PROCESS AND APPARATUS Fort rostrum.

TAPERED srsns Edmund B. Cairns, Naugatuck, Conn assignor to Cairns Metals Corporation, a corporation of New York I Application July 25,1936, serial No. 92,551

11 Claims. (onto-19 Thepresent lnvention is directed to apparatus which. pparatus preferably combines several and a process for producing tapered structural etal working operations, such as drawing, members and the resultant product. Such ta- Swagihg d orging. I have found this appapered metal structural members have many uses ratus to be l f r p y formin sp r suitand are particularly adapted for usaas spars, able m assembly and at a 10W unit eestribsand struts in thefabrication ofairplanes and More e ly y preferred apparatus intheir parts I V cludes a pair of freely rotating rollers having a The airplane industry has, during recent years, mined spacing. Between these rollers endeavored to substitute parts made of light metthere is dapted. to pass a blank and a forming lo als and their alloys for parts previously made of element apable of'constantly varying the worknon-metallic substances. While such light metals i s ance ween the co p a i s. One may have far' greater strength by volume than of the cooperating r0118 y e, as is shown in. the materials previously used, they are also charmy Preferred form. a 0mp1ementary groove coacterized by a greater weight. It is therefore deacting W h forming element.

'15 sirable that the metallic structural elements Preferably the P d i n of aircraft wing should bereduced to a size and weight compa- Spare e rming element 01- th d bar is of rable with material replaced, without sacrificing generally ngular cross-sectional shape. The strength. Furthermore, it is highly desirable to complementary groove in the roll is f a v-shepe, obtain metallic elements of uniform strength. the angle the Walls of they -Shape groove Inasmuch as the metals from which the elebeing less than the angle at the apex of the tri- 20 mentg are fabri t d are usually more expensive angular forming'eleinent. I have found in some than the materials of the structures replaced, it is Operations h a sirable spacing between the preferable that the metal elements be fabricated e of the triangular forming member and the shnply at low unit cost and with a minimum bottom of the groove at least at the beginning of cess of metal present. the operation upon the blank may be a distance 25 s metals for example, as aluminum, magsubstantially equal to the thickness of the metal nesium, and stainless steel alloys are diflicult to blank i g s aped. Work as they are not susceptible to rolling proc- A Strip having a preliminary n itudinal taper essesc'ommonly used in working iron and steels. in W h 1 usually d as th Starting kan The vmetals tend to crack and tear during the The pr l minary tap r g v nr t s strip is pref.-

ordinary rolling and bending action. Also such ably such t at when t pass through e o ls a rolling action tends to produce a crystalline iring the taperin thi h e is no ex structure in the metal which is neither uniform e Ve increase in the width of the finished elenor sufficiently rearranged to give desired maxihient pa O end to end. The strip'ls drawn mum and uniform strength characteristics ut 0 h there y be, material n r in 35 thrugh t m t length. By using a blank charge tapering in The present invention has for an object the width, the internal stress on the strip is gradualproduction of light metal or metal alloy struc- 1y reduced as the narrowing strip passesethrough tural elements having a cross-sectional shape the rolls thus tending to reduce the possibility of 40 best calculated to withstand and distribute extending or stretching the metal beyond its elas- 40 stresses applied thereto and without excessive tic limit. weight.- The action and the eflect of my treatment on A further object of the invention is to produce the structure and shape of the metal blank is simstructural elements which are tapered lengthwise ilar to a die'E' d a n i bending and 4 inprder to reduce their weight and at the same svvaging treatment. time retain sumcient thickness at the points of As contrasted with a drawing treatment in greatest stress to be able to withstand without which the metal is caused .to flow axially, only, of distortion the maximum calculated stresses apthe die, my treatment causes the metal to flow plied thereto. transversely as well as axially of the blank, pro- 5 A further object' of the invention is to produce ducing a structure in which the metalcrystals are a process and apparatus for economically and relatively angularly disposed, thereby greatly uniformly producing such structural elements. Strengthening and teughenihg e Structure To achieve the objects of the invention, I have member formed. developed an apparatus for forming structural As, compared to a forgingoperation, where an elements for example, spars from metal blanks, interlacing crystalline structure is produced by Ill! repeated localized flowings of the metal under impact, my process produces a generally uniform flowing of the metal, thereby resulting in a homogenous structure. Also I am able to form the spars or structural members at a much higher rate of production than would be possible with a forging treatment.

As compared with a bending operation which would unavoidably produce cracks and tears in the metal adjacent the bend, my treatment causes the metal to be forced toward the bending'line. This flow of metal eliminates cracks and fissures along the bending'line. In effect, the flow of the metal in my treatment is counter to the direction of flow of metal in a bending treatment and the metal is therefore bent under compression rather than under tension.

My apparatus is especially suitable for forming structural elements which taper in cross-section both as to overall depth and .to thickness of the metal having a V-shape in cross section. These spars are particularly suitable for use in aircraft. The wider end of a blank is fixed adjacent the end of the forming and supporting 'mechanism permitting the greatest working disand downwardly in the groove also takes place substantially without restraint. This flow as is shown may be utilized to form beads on the edges of the finished spar by providing appropriate grooves in the forming element or draw'bar. The

,fiowing of the metal into the bead edges avoids the formation of cracks at the edges.

With my apparatus it is also possible to form bosses of any desired shape or thickness along the length of the spar for example, by appropriately providing-the forming member with depressions or abutments.- These are preferably adjacent the bead grooves but may be placed where desired, for example, inthe apex.

My apparatus may also be utilized to produce longitudinally curved and preferably tapered structural elements by making the forming member curved gradually from end to end.

For a better understanding of the invention reference may be had to the accompanying drawings in which:

Figure l is a plan view of my spar forming device;

Figure 2 is a side elevation of the spar forming device;

Figure 3 is an end view of the forming rolls with the draw plate and forming element shown in section;

Figure 4 is a partly broken sectional view taken on line 4--4 of Figure 2 showing a guide for the blank;

Figure 5 is a perspective view of a portion of one form of spar produced by my process and apparatus;

Figure 6 is a perspective view of a tapered blank prior to forming, partly broken away;

Figure 7 is a perspective view of a draw plate and one form of forming element, partly broken away;

Figure 8 is a diagrammatic view of a modified type of forming device having a furnace and a gas chamber thereon; and

Figure 9 is a side .view of a portion of a modified form of draw bar and forming element.

Illustrative of one embodiment of my invention, Figures 1, 2 and 3 disclose an apparatus suitable for forming and shaping a metal blank A (Figure 6), into a spar B (Figure 5) substantially V-shaped in cross-section and tapering overall in metal thickness. The blank A may be cut or formed in a tapered form lengthwise.

The blank A may be shaped and formed over a generally triangular forming member 2. This forming member may be integral with or rigidly attached to a base 4 which tapers in the thickness from end to end as best shown in Figure '7. The wider end of the blank A may be attached to the triangular forming member 2 by means of cooperating pins 6 and apertures 8, the end of the blank A being conformed to the shape of the forming member by any suitable means, such as forging or swaging, the remainder of the blank A merely resting on the apex of the forming member 2. The draw bar 4 and attached blank A are than placed upon a table or support l0 provided with a plurality of supporting rollers l2 which allow the draw bar to be drawn along the table by any suitable means, such as chains I 4, attached to the ends of the draw bar 2 and passing over sprockets "5. Cables and a winding drum may be readily used instead of chains and sprockets for advancing the forming member, if desired. Any suitable power means (not shown) may be used to draw the blank A between freely rotatable rollers I 8 and 20, the latter acting as a support for the draw bar 4. The forming rollsl8 and 20 are rotatably mounted in a heavy framework 22, the roll l8 being adjustable relative to roll 20 through the medium of screw-threaded shafts 24 swivelled in sliding journal blocks 26 carrying the roll supporting shaft 28.

The shaping roll l8 may beprovided with a peripheral groove 30 of generally V-shape, the walls of which are inclined at a slightly less angle than the angle of the walls of the triangular forming member 2. When a blank A is drawn under the roll l8, the blank wfll be pressed,

drawn, bent and forged, and caused to elongate and flow upwardly and downwardly between the walls of the roller groove 30 and the triangular r member 2, as previously described. The upper roller I8 is preferably adjusted so that the distance between the bottom of the groove 30 and the apex of the forming member 2 is substantially equal to the gauge of the blank A.

The edges of the spar may be readily provided with a flashed bead by providing the forming element 2 with a longitudinally extending groove 32 (Figure 7) into which the metal of the blank is caused to flow because of the tapered groove between the roller l8 and forming member 2. If desired, the groove 32 may be inclined slightly to the axis of the forming member, in accordance withthe taper in width of blank A.- This groove acts to form a bead 34such as is shown in Figure 5. Likewise the forming member 2 may be provided with a series of depressions 36, shown in dotted lines on Figure 7, whereby bosses 38 will be formed on the interior of the spar B to compensate for metal removed when screw, bolt or rivet holes 40 are drilled therethrough. Likewise, such bosses may extend below the beads and are produced by providing depressions, such as 42, at the edges of the flash grooves 32.

It should be noted that there is no means provided for restraining the flow of the metal of blank A inthe groove between roller l8 and forming member 2. The metal may flow in such a manner that a uniform crystalline'rearrangement may be brought about and uniform stresses are set up throughout the finished spar. This action difiers from the usual molding and rolling operation.

While a number of the lighter metals and alloys may be shaped in a cold state, such metals as magnesium and stainless steels are preferably worked in a heated condition. A suitable temperature for working magnesium is in the vicinity of 450 F. and for working stainless steel is in the vicinity of 1650" F. For heating these metals 'prior to working, I have provided a muille furnace 44 ahead of the shaping rollers l8 and through which the-blanks A and draw plate 4 and forming element 2 are passed to bring the blank A to the desired temperature. While any desired heating means may be utilized I have disclosed an electric heater 46. Also, if desired the shaping roller It may be provided with heating means, although generally this-is not necessary.

To prevent scaling of the metal, due to the heat of working and oxidation of the surface, I may also provide the device with a jacket 41 through which or into which a non-oxidizing gas may be passed.

A particularly suitable means for guiding the blank A intoand through the forming rollers, without placing any restraint thereon, or restricting flow of the metal while shaping, is disclosed in detail in Figure 4 and as applied to the apparatus in Figures 1 and 2. The guidingmeans shaft 56 may be rotated mechanically by any suit- V able means, but I have illustrated it as being manually rotated by a knob 56.

While I have disclosed the shape of the spar B as being generally of a V-shape incross-section,

it will be understood that it may be made L- shaped or U-shaped without deviating from the invention. Also as shown in Figure 9 of the drawings, the draw bar 61 may be formed with a curved upper surface 68 which converges toward a plane lower surface 69. The forming member 10 is likewise curved to conform to the surface 68 of the draw bar 51 and is of uniform crosssectional shape throughout its length. The forming member II! has grooves H therein for forming beads on the edges of the structural member.

It will be understood that the blank A may be varied in shape, such as by decreasing its thickness by tapering on straight or curved lines from end to end and that the width of the bar can be tapered from end to end likewise on curved lines.

members, comprising a freely rotatable forming roll, an annular groove in theroll, a draw-bar having a longitudinal. taper from end to end, a forming member fixed to the draw-bar substantially complementary to the groove in the form-' ing roll .and of substantially uniform cross-section throughout its length, means for supporting the draw-bar for movement beneath the forming roll, means for fixing a stripof metal to one end of the draw bar and-means for moving thefdrawbar axially with the forming member in ..but

spaced from the roll groove, whereby the spacing" i between the bottom of the groove and the top of tithe forming member will va'ryinversely as the taper of the draw-bar and the strip of metal will be bent, expanded longitudinally and transversely and metal will be caused 'to flow toward the edges of the{ strip and to the zone of bending.

2. An apparatus for making tapered structural members, comprising a freely rotatable. forming roll having a circumferential groove therein, a

forming member having a cross-section generally complementary to said roll groove with the faces of the forming membernfit a greater angle than the sides of the groove, eans' for fixing one end of a strip of metal to the forming member at its leading .e'nd, means for movin'g the forming element axially and adjacent the roll in such relationship that the strip is worked between the' faces of the forming element and the sides of the groove and allowed to expand-longitudinally and transversely and means for gradually decreasing the working distance between the forming element and the roll as the forming element moves. 3. The device set forth in claim 2 comprising a pair of adjustable jaw members disposed on opposite sides of and in the plane of the top of the forming member and means for adjusting the jaw members to .engage and guide the strip of metal into the working zone between the roll and the forming member.

fixed to said draw bar, said forming member having across-section generally complementary to said roll' groove with the faces of the said forming member at a greater angle than that defined by the sides of the groove, means for fixing a metal strip to be worked to the forming member at the zone of least efiective thickness of the draw bar, means for moving the draw bar amally and in'working relationship to the roll, said roll and forming mechanism being in, such relationship that the metal strip being worked is free to expand longitudinally and transversely.

6. An apparatus for making tapered structural members, comprising a. freely rotatable forming roll having a generally ll-shaped circumferential groove formedtherein, a draw-barhaving a varying efiective thickness from end-.to end, a

roll groove with the angle formed by the faces of said forming member greater than that defined by the sides of said groove, said forming member and said grooved roll being in such r'elation that a metal strip on said forming member is free to expand transversely andlongitudinally, means for fixing a metal strip to be'worked to said forming member at the zone of least effective thickness of -said draw-liar means for supporting the draw-bar for movement 'beneath the forming roll, and means for moving the forming Im'ember axially and in' working relationship to the roll groove.

7. The method of making tapered structural members, which comprises fixing a metal strip at one end to a forming member, bending the metal strip along alongitudinal line, progressive-4 ly increasing the amount of working upon the strip sumciently to cause a flow of metal away from said fixed end of said strip while permitting free expansionv of metallongitudinally, maintainmembers which comprises fixing a metal strip at one end to a forming member, bending the metal strip along a'longitudinal line, progressively increasing the amount of working upon the strip sufliciently to cause a flow of metal away from cumferentialgroove therein which is generally complementary to the forming member with the angle between the sides of the groove being less than the angle between the faces of the forming member, forcing the strip into the groove in the .roll to work and bend the strip along a longitudinal line and causing a flow of metal to the zone adjacent the bending line and toward the edges while allowing flow of the metal both transversely and longitudinally and gradually decreasing the working distance between the forming member and the roll to taper the strip longitudinally.

10. The process set forth in claim 9 which comprises heating the strip during its movement relative to the roll.

11. The process set forth in claim 9 which comprises heating the strip in an atmosphere of inert gas during its movement relative to the roll.

EDMUND B. CAIRNS. 

